The present invention relates to implantable stimulation devices, e.g., cochlear prosthesis used to electrically stimulate the auditory nerve, and more particularly to an electrode array for use within an ossified cochlea in conjunction with a cochlear stimulation system.
Hearing loss, which may be due to many different causes, is igenerally of two types: conductive and sensorineural. Of these, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that acoustic information does reach the cochlea and the hair cells. Some types of conductive hearing loss are also amenable to alleviation by surgical procedures.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This type of hearing loss is due to the absence or the destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. These people are unable to derive any benefit from conventional. hearing aid systems, no matter how loud the acoustic stimulus is made, because their mechanisms for transducing sound energy into auditory nerve impulses have been damaged. Thus, in the absence of properly functioning hair cells, there is no way auditory nerve impulses can be generated directly from sounds.
To overcome sensorineural deafness, there have been developed numerous cochlear implant systemsxe2x80x94or cochlear prosthesisxe2x80x94which seek to bypass the hair cells in the cochlear (the hair cells are located in the vicinity of the radially outer wall of the cochlea) by presenting electrical stimulation to the auditory nerve fibers directly, leading to the perception of sound in the brain and an at least partial restoration of hearing function. The common denominator in most of these cochlear prosthesis systems has been the implantation into the cochlea of electrodes which are responsive to suitable external source of electrical stimuli and which are intended to transmit those stimuli to the ganglion cells and thereby to the auditory nerve fibers.
A cochlear prosthesis operates by direct electrical stimulation of the auditory nerve cells, bypassing the defective cochlear hair cells that normally transduce acoustic energy into electrical activity in such nerve cells. In addition to stimulating the nerve cells, the electronic circuitry and the electrode array of the cochlear prosthesis performs the function of the separating the acoustic signal into a number of parallel channels of information, each representing the intensity of a narrow band of frequencies within the acoustic spectrum. Ideally, each channel of information would be conveyed selectively to the subset of auditory nerve cells that normally transmitted information about that frequency band to the brain. Those nerve cells are arranged in an orderly tonotopic sequence, from high frequencies at the basal end of the cochlear spiral to progressively lower frequencies towards the apex. In practice, this goal tends to be difficult to realize because of the anatomy of the cochlea.
Over the past several years, a consensus has generally emerged that the scala tympani, one of the three parallel ducts that, in parallel, make up the spiral-shaped cochlea, provides the best location for implantation of an electrode array used with a cochlear prosthesis. The electrode array to be implanted in this site typically consists of a thin, elongated, flexible carrier containing several longitudinally disposed and separately connected stimulating electrode contacts, perhaps 6-30 in number. In a non-ossified cochlea, such electrode array is pushed into the scala tympani duct to a depth of about 20-30 mm via a surgical opening made in the round window at the basal end of the duct.
Ossification is the formation of bone tissue. An ossified cochlea is thus a cochlea wherein the scala tympani duct, and/or other ducts within the cochlea, are filled completely or partially with bone growth tissue. Needless to say, it is not possible to insert an electrode into an ossified cochlea using conventional insertion techniques because the bone growth tissue blocks such insertion. Thus, there is a need for an effective cochlear electrode system which can be used for patients with ossification, whether such ossification only extends to the first turn of the scala tympani duct (partial ossified cochlea) or whether the ossification fills the entire scala tympani duct (fully ossified cochlea).
The present invention addresses the above and other needs by providing an electrode system for insertion into an ossified cochlea. Heretofore, there have been no electrode systems of which applicants are aware that have satisfactorily been useable with an ossified cochlea. Thus, heretofore, those patients having an ossified cochlea have not been able to benefit from implantation of a cochlear prosthesis.
The electrode system of the present invention includes a first electrode array and a second electrode array, both of which are electrically connected to a suitable implantable cochlear stimulator (ICS). Each of the two electrode arrays has a plurality of spaced-apart electrode contacts thereon, e.g., eight to twelve electrode contacts on the first electrode array, and six to eight electrode contacts on the second electrode array.
Where the cochlea is partially ossified, e.g., only up through the first turn of the scala tympani duct, a straight tunnel is drilled through the bone formation in the ossified scala tympani. This tunnel typically has a diameter of approximately 2 mm and a length of about 8-10 mm. The first electrode array is then inserted into this straight tunnel. The second electrode array is then placed through an additional cochleostomy drilled at the beginning of the second turn of the cochlea. An electrode positioner of the type disclosed in applicant Kuzma""s copending patent application, Ser. No. 09/140,034, filed Aug. 26, 1998, incorporated herein by reference, may be used with this second electrode in order to assure that the second electrode hugs the modiolus of the cochlea as much as possible.
Where the cochlea is completely ossified, e.g., ossified through the second turn of the cochlea, a second tunnel is drilled through the ossification at the second turn of the cochlea, and the second electrode is inserted into this second tunnel. As needed, an electrode positioner may be inserted with the second-electrode in order to assure that the second electrode hugs the modiolus of the electrode.
For some patients, depending upon the degree of ossification, it may be desirable to insert the one or the two electrodes into a tunnel drilled in the ossified scala tympani, as described above, and to insert the other of the two electrodes into the scala vestibule.
It is thus an object of the present invention to provide an electrode system that may be used within an ossified cochlea.
It is an additional object of the invention to provide such an electrode system that, when used with a cochlear stimulation system, affords a patient having an ossified cochlea the opportunity to hearxe2x80x94an opportunity which heretofore has not been possible.